1. Technical Field
The present invention relates to a feed-off-arm type sewing machine for flat seaming provided with various kinds of drive mechanisms including a needle bar drive mechanism, in a head unit arranged adjacent to an end portion of a sewing machine arm which incorporates a sewing machine main shaft.
2. Description of Related Art
For example, a feed-off-arm type sewing machine for flat seaming used for seaming of crotch portions of briefs and shorts, is provided with a sewing machine arm and a sewing machine bed extending in directions which are different from each other in an upper part and a lower part of a sewing machine frame, respectively (see, for example, Japanese Patent Application Laid-Open No. 7-57272 (1995)). A head unit is arranged adjacent to an end portion of the sewing machine arm in a direction substantially orthogonal to said sewing machine arm. A plurality of needles are mounted on a lower end of a needle bar which hangs from said head unit towards a tip of the sewing machine bed, and a presser metal is mounted on a lower end of a presser bar which is in proximity to the needle bar and hangs from the head unit.
Seaming by such a feed-off-arm type sewing machine for flat seaming is performed by the procedure of superimposing edges of two sheets of cloth to be seamed one on the other over a predetermined width, holding the edges between the presser metal mounted on the lower end of the presser bar and the sewing machine bed, feeding the cloth from a proximal side of the sewing machine bed towards a tip side thereof by an operation of a feeding mechanism located inside the sewing machine bed, and seaming the edges together by a coordinated operation of a plurality of needles which move up and down with the needle bar, and a looper located inside the sewing machine bed.
The needle bar is connected with a tip of a needle bar lever extending in the head unit from the inside of the sewing machine arm. The needle bar lever is a swinging lever which swings about a horizontal axis by transmission from a sewing machine main shaft incorporated in the sewing machine arm. The needle bar is constructed such that the needle bar moves up and down according to swing of the needle bar lever.
A transmitting mechanism for a top cover thread hook arranged above the presser metal, a knife provided in a part of the presser metal, or the like is arranged within the head unit. The transmitting mechanism is provided with a rotating member which penetrates a lower wall of the head unit inside and outside, and rotates about a vertical axis. A tip of an actuating rod extending in the head unit from the inside of the sewing machine arm is coupled with the rotating member. The rotating member is repeatedly rotated by reciprocation in an axial direction of the actuating rod by transmission from the sewing machine main shaft. This repetitive rotation is transmitted to said top cover thread hook or said knife, thereby causing the top cover thread hook or the knife to perform a predetermined operation.